Check Leap Year

by isuru_nan

HTML

<!doctype html>
<html>
  <head>
    <meta charset="utf-8" />
    <meta name="viewport" content="width=device-width" />
  </head>

  <body>
    <form name="theForm" onsubmit="return checkLeapYear()">
      Year: <input type="text" name="year" />
      <input type="submit" value="Submit" />
    </form>

    <script>
      function checkLeapYear() {
        var yearValue = document.forms["theForm"].elements.year.value
        
        if (yearValue === "") {
        	alert("You must enter a value");
        	return false;
        }
        
        if (isNaN(yearValue)) {
          alert("Not a valid number")
          return false
        }

        var year = parseInt(yearValue)
        
        if (year % 100 === 0 && year % 400 === 0) {
			alert(year + " is a leap year");        
			return false;
        }
        
        if (year % 100 !== 0 && year % 4 === 0) {
			alert(year + " is a leap year");
			return false;
        }
        
		alert(year + " is not a leap year");
        
        return false
      }
    </script>
  </body>
</html>